Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl> writes:
> I think it takes a lot of concurrency for
> the situation to arise.
Maybe. Since Peter can reproduce the error, there's not any concurrency
misbehavior involved in VACUUM itself; what we are dealing with is
probably corruption in the on-disk state of the index (or maybe a legal
corner case that _bt_pagedel mishandles). There might have been
concurrency to blame for getting into that state in the first place.
Need data ...
regards, tom lane